Unfortunately I can't see which pins are driven by the variables fan and heater.
Looking at the program, you want to turn both either completely on or completely off.
Instead of turning them on/off with a digitalWrite() you're using analogWrite(), which is possible.
AnalogWrite doesn't work with all pins though, it's meant for PWM-pins only.
In the first case you use analogWrite() correctly by sending a value of 0 or 255, but the heater is driven by a HIGH and a LOW. I haven't tried to see whether that is possible, but it would be better IMO to use a number instead or go for the digitalWrite-command.